Defrosting system



Feb. 17, 1953 F. w. POWERS ET AL 2,628,479

DEFROSTING SYSTEM Filed Oct. 2, 1950 .Zv VENTO/QS: 24 /x 14/ Pan/25 A4 5507 L u/vw/v w, Fatal Patented Feb. 17, 1953 UNITED STATES ATENT OFFICE DEF-HOSTING SYSTEM Application'0ctober-2, 1950, Serial No.'188,026

'13'Claims. 1

This invention relates to mechanical refrigerating apparatus and more particularly to :the provision in such apparatus of improved defrostingmeans to remove excessive accumulations of frost and ice'fromthe evaporator .orchilling unit thereof.

Such chilling units or .evaporators, which are frequently in the formof pipe coils, may .rapidly accumulate ice and frost :on the exterior surfaces thereof when operated .below freezing tem-. peratures. As the'thickness of such deposits ,increase,the-coo1ing surfaces become insulatedzand unable -to abstract heat from .the surroundin medium, "thus progressively reducin operating efficiency. Frequent removal of this iceand frost coating, which operation is commonly known in th art as defrosting, is therefore required in order to maintain the efficient functioning of the refrigerating apparatus.

When its becomes necessary to defrost such cooling surfaces as are contained in theordinary household refrigerator, vthe refrigerator :compressor isshutoff, allowing the temperature of the refrigerant within the evaporator to rise above freezing, and the iced-surfaces may be simultaneouslyexposed to the warmer outside air until the *icemelts and runs oir" the :coils. Obviously this method is not suitable for defrosting in commer- -cial-p1ants since it requires too much time as well as the intermittent exposure-of the contents of' the refrigerated area to undesirable hightemperatures. In commercial :type refrigeration sys- "tems various methods-of defrosting by the use of watersprays have heretofore been suggested but theyhave involved the disadvantages of complicated equipmentand-eXpensi-ve installations, particularly to provide for drainage and in the means employed for preventing freezing of water used for defrosting during nonde'frosting periods.

Other means which have heretofore been employed'in -the defrosting of commercial size refrigeration units include the use of heated-refrigerant gases circulated from the compressor directly through the evaporator, the' heate'd gases eventually raising the temperature within the cooling coils until the exterior :frost -or :ice is melted. This method isv disadvantageously slow and time-consuming :due to the relatively slow theat transfer :between the heated gaseous medium and :the cooling coils and usually results in :cOnsiderahIe rise'in temperature in the refrigerated area during the long defrosting period.

It is an object of .our invention .to provide .an improved system for defrosting of low tempera- --turerchilling units which will servevto quickly and rapidly i heat such ichilling units to atemperature operate.

discussion of-the drawing, and in ch:

2 just suificient to coars the exte o frost-amide? to melt or drop coir-ther b defrost n t apparatus a minimum pe i d of t m ah h t permitting a substantial rise in temperature f the refri erated ar a d ri th -defrostin e m.

Our inventi n contemplat s "th u o eatin means o el vate th pe atureetasliquidrsiieh as the liquid refri erant, wh n ldei estin i quiresi, and ther ir ulation f h at. iiid throu h the ool n coil rah dlyeler t the tempera ure of th latter ir0m-,the-ins J it until the excessive frost a diee aremelteiaad drop therefrom- A further object of ourinl/ention sthe ;p rovision of a defrosting system i ,7 liquid may e intermittentl ,c ciile r oli g element of arefr erator e. .or eoo1'r,efrigmh :;f "9nl the ,Gfilldfil fifir shut off.

A further obje f our invention Izi tnspz imdde a va1ve-c0ntro11ed cond i s em, iqi F1333 P and liquid heating m ans ,conneci dz nt 4a 8- fri r ion yst m in su h aazm hne .zfrigerating medium may be ca sed continuously :between the liquid he g iin ans z nd'the cooling cells during the defrostingoper- ,compressor commonly employ d ;1 h 33313? rating cycle.

.;A furtherobject isto providecinga.ref a i m app ratus ofzthe aforeme ioned character-eeritriealhea in elemen dish r .A relationship with the liquidi e rrieere harder to elevate the temperat r of th at hfp sir i ulation throu h -the;c.0p ir. e-e0ils; i1 hen tierf-msti-n cycl .A 'ifurther object is t provide a re ri e at n syst i w ch the t m ature t w ic iquid refri eran is he edinfh de ies, n

within the liquid heating means or thepressure w th n e e iee 'an i qui ta reaeh'e p determined level.

:entadditional ebi e the-provis on .:o.,f ;a.zdefrostin system which :is efficien ,i aoneratien. rel l i exp n i t ta vsq id ,.-imnl @1 9 still furth r bj t an aspe t :of the-r nveh-tion wi1le0m apparent inv-th si hon n fig. ;1 is ;a semidia rammatic :eley ti hal .yliew 12f aprefri eratin system embodyin he s een- 1911- "The lrefrigerating apparatus. shown mmprises the flow of the liquid refrigerant, sections 3| include an inlet conduit section am,

a refrigerant compressor l0, driven by means of a motor II, which evacuates refrigerant vapor such, for example, as ammonia vapor or Freon, from a refrigerant liquid tank l2 through a suction conduit [3 having a manually operated normally open shutofi. valve I4. The compressed vapor from the compressor [9 is forced through a condenser l5, where it is cooled and condensed under relatively high pressure to the liquid phase, in accordance with conventional operation, and is led through a conduit [6, having a solenoid operated shutoff valve ll disposed therein, to the refrigerant liquid tank l2. The conduit [6 extends within the tank to a lower portion 12a thereof where the refrigerant liquid is discharged into the tank under reduced pressure.

A liquid pump [8 driven by a motor [9 connected through a manually operated starting switch 20 to a source of power (not shown), pumps the refrigerant liquid from the lower portion [2a of the tank 12 through a conduit 2| to an inlet I 8a of thepump and thence, from an outlet'l8b thereof, through a conduit 22 to a liquid distributor header 23. Disposed in the conduit 22 between the liquid pump l8'and the liquid distributor header 23 is a normally open, manually operated shutoff valve 24. The liquid distributor header 23 receives the liquid under reduced pressure and discharges same into a plurality of cooling coils 26 on which ice and frost will accumulate in normal operation upon circulation of the liquid refrigerant therethrough during the cooling cycle.

The defrosting apparatus includes a liquid heating means, illustrated generally at 28, having a plurality of electrical heating elements 29 interposed in heat transfer relationship with the liquid refrigerant between the liquid pump l8 and the liquid distributor header 23. Each such heating element 29 is disposed within a relatively small diameter tube 30, which may be filled with a fluid, as, for example, oil, and secured within a larger diameter conduit section 3|, the annular space between the tube 30 and the conduit section 3| providing a passageway for The conduit a plurality of intermediate conduit sections 3lb and an outlet conduit section 3Ic which are joined in series by connecting conduit sections 32 in order to provide a continuous sinuous passage or coil for the flow of refrigerant liquid from an "inlet conduit 33 leading from the outlet I8b of the fluid pump I 8, to inlet conduit section 3m and thence to an outlet conduit 34, leading from the outlet conduit section 3lc back to the liquid distributor header 23. Disposed in the inlet conduit 33 is a normally closed, manually operconductors arranged in a closed circuit and adapted to heat up when an electric current is passed through the circuit. As illustrated in the drawings, current is supplied to the heater ele- 'ments through conductors 38 which are connected through the contacts of a normally closed relay 39' and a manually operated switch 49 to a three-phase source of electric power (not shown).

The relay 39 comprises a relay switch 4| and a relay coil 42, the former serving to connect or interrupt the flow of electrical energy to the heater 4 elements 29. The relay coil 42 is connected in series with a normally open thermostatic switch 44 and also a normally open pressure switch 45,

- the switches 46 and 45 being connected in parallel with each other to a source of power that may conveniently be obtained from any two of the conductors 38.

The flow of liquid refrigerant into the refrigerant liquid tank is controlled by means of the solenoid operated shut off valve [1 which is connected by conductors to a source of power (not shown) through a float regulator 48 in which the liquid is maintained at an equal height with the liquid level in the refrigerant liquid tank I2 by'means of the bleeder conduits 49 and 50 which lead from the lower and upper portions respectively of the float regulator 48 to the refrigerant liquid tank l2.

The operation of the defrosting system of our invention is initiated when the cooling coils 26 become coated with ice or frost, during the conventional cooling cycle, to an extent that the withdrawal of heat from the surrounding air in the refrigerated area is reduced to an ineificient operating level. Th switch 40 is first closed in order to supply current through the conductors 38 to the heating elements 29 which in turn heat up the tubes 30. Theliquid heating means 28 is thus prepared for the transfer of heat to the liquid refrigerant as it is by-passed therethrough. Prior to opening such by-pass liquid circuit, the valve I 4 is closed in order that no refrigerant gases can be pulled back to the compressor through the suction conduit I3, thereby stopping the cooling cycle.

With the liquid pump [8 remaining in operation as in th cooling cycle, the valves 35 and 36 are opened and valve 24 is closed. This operation causes the liquid refrigerant from the refrigerant liquid tank [2 to travel through the conduits 2 l, 22 and 33 to the liquid heating means 28 via the inlet conduit section 3Ia, thence through the intermediate conduit sections 3Ib, via the connecting conduit sections 32, to the outlet conduit section 3lc. From the latter the refrigerant liquid is led via outlet conduit 34 to the liquid distributor header 23, from which it is circulated through the cooling coils 26 back to refrigerant liquid tank l2.

During the passage of liquid refrigerant through the liquid heating means 28, the temperature of the former is rapidly elevated by transfer of heat from the tubes 30 to the refrigerant liquid flowing in the annular space between the tubes 39 and the conduit sections 3|. Subsequently as the heated refrigerant is circulated through the expansion coils 26, heat is transferred to the coils from the refrigerant, elevating the temperature of the latter from the inside out until the excessive frost and ice are melted and drop from the coils. A portion only of the liquid refrigerant will vaporize to the gaseous phase at such elevated temperature during the passage thereof through the cooling coils 26 While the balance will be accumulated in the lower portion l2a of, the tank I2 for reheating and recirculation through the coils 26. Such refrigerant as vaporizes will accumulate in the liquid refrigerant tank buildin up the pressure therein and in the coils 26, which increased pressure will in turn tend to reduce further vaporization and maintain the re- When the temperature of the liquid refrigerant, near its point of exit from the liquid heating accumumeans 28, reaches a predeterm'inedvaluerequisite toef'fec't the melting-of iceand frost on thecodling coils 26 as aforesaid, the thermostatic switch 44 automatically closes, completing the circuit from the relay um 42 tothesource-of power (not shown) and energizing the former, thereby opening the relay switch 4! of the relay 39. The-circ'uit to the heatingelements 2-0 through conductors 38 being 'thus interrupted---and the liquid heating means deactivated, 'th'e' temperature of the refrigerant liquid is elevated no f-urther until the temperature switch ll i reopens under :the influenceof the liquid refrigerant cooled to a :lower temperature; In this manner-thetempera'ture of the liquid refrigerant in the cooling coils .26 is maintained within predetermined limits so that the cooling coils are heat'ed only to a .minimum temperature "sufficient to oauseizmelting L'of accumulated frost and ice, preventing tunnecess'ary elevation of the temperature of thearea refrigerated the'reby.

The pressure switch 45 :also: serves its interrupt the :current fiowjo itheaheating elements :29 by energization iof :the .relayicoil 42 and opening of the relay switch "4! when theipressurenf refrigerant vapor -within the refrigerant liquid .tank reaches .a certain predetermined safety limit. Thus the accumulation of excessive pressure Within the tank 42 will terminate the heatingzof the liquidrefrigerant andithje further building up ofsuchlpressure due-toithe increased tendency :of the refrigerant to vaporize inathe cooling coils '25 when heated. Upon opening of theshutofi valve M .andwithdrawalof the excess refrigerant gases to the compressor H), the pressure within the tank 12 :may :be reduced :below the safety level, whereupon the pressure switch 4.5 will open to remake the circuit to the heating elements 29,.

To maintain :the proper supply :of refrigerant liquid "within the-tank 12,,-the solenoid operated shutoff valve I! is disposed within the conduit l6 and is automatically opened by means .of the float regulator 58 when the liquid level within thetank il2 falls .below a set level to permit the entry into the tank I? of additional refrigerant from the compressor 1.0 -or, conversely, itxi'szcl'osed thereby when :such liquid level reaches a-given height.

Theioperation in th'e defrosting cycle is continuednntil .all'theffrost and ice are melted from the evaporator coils 26 and until the water caused by melting has run nth-whereupon the defrosting cycle is terminatedand .the cooling cycle is reestablished by opening thesw-itch 4:8 to .disconnect heating elements 29, opening the valve H, closing thevalves 35 and *36, and opening the valve 24. The refrigerant will then be led from the compressor 10 through the condenser 45, Where it is cooled under pressure, to the -refrigerant. :iiquid .tank .l..2, .f.rom which it is pumped to the liquid distributor header 23 and thence through the :cooling coilsiB in .the conventional refrigerating cycle.

it 'is apparent .that have devised -a defrosting system wherein the-refrigerant .in liquid formz-may be intermittently heated in a short period of time and circulated through the cooling coils, thus providing for rapid elimination of accumulated ice and frost in a minimum period of time during which the refrigerated area is exposed to elevated temperatures.

While we have disclosed an exemplary embodiment of our invention herein for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated therein -withoutdeparting ;from:tlie

spirit of 'the invention.

We claim as our invention:

1. In a refrigerating system :including va zoom-v pressor normally forcing refrigerant avapornnder pressure through a condenser :where it is cooled and condensed to the liquidipha'se andr; then:dis-.

charged into a refrigerant liquid tanklunderireduced pressure from :which .it is fpumped by ;:.a liquid pump to a liquid tdistributor header from which it is circulated through cooling coils backthe outlet-of the liquid'pump; an-outl'et conduit.

connectingsaid liquid heating means and .the;liquiddistributor header; and valve meanscontrolling the flow of refrigerant liquid fromthe liquid pump through said inlet conduit through .said liquid heating means and said outlet .conduit to the liquid distributor header. I

:2. Ina refrigerating system including a compressor normally forcing refrigerant vapornnder pressure through a condenser where it is cooled and condensed to the liquidphase-and then discharged into a refrigerant liquid tankunder .reduced pressure from which it is pumped by va liquid pump to a liquid distributor header from which it is circulated through cooling coils back to the refrigerant liquid tank, the combination of electrical heating means connected ,in'hea't transfer relationship between the outletmo'f said pump and said liquid distributor header adapted to elevate the temperature of .the liquid refrigerant circulated through the cooling coils to'melt accumulated ice and frost thereon; an inlet conduit connecting said liquid heating means "and the outlet of the liquid pump; an outlet conduit connecting said liquid heating means and the liquid distributor header; and valvem'eanscontrolling the flow of refrigerant'liquid from'the liquid pump through said inlet "conduit-through said liquid heating means and saidoutl-et conduit to the liquid distributor header.

3. A refrigerating system as defined inclaim2 in which said electrical heating means has'con nested thereto a thermostatic switch adapted "to inactivate said heating means when the'temperature of thefrefrigerant liquid therein rises above a predetermined level. v

4. -.A. refrigerating system as defined in claim? in Which the refrigerant liquid'tank has'a pressure switch connected thereto, said pressure switch being connected to said electricalheating means for deenergizing the latter when-the pressure within the refrigerant liquid tank reaches a predetermined level.

5. A refrigerating system as :defined'in claim 2 in which said electrical heatingme'ans includes a sinuous fluid conduit in'which'is disposed a plurality of tubular electrical "heating elements defining annular passageways between said sinuous fluid conduit and itheexterior surfaces thereof.

6. In a refrigerating system'including 'a compressor normally forcing refrigerant vapor under pressure through a condenser where it is cooled and condensed to the liquid phase and then discharged into a refrigerant liquid tank under reduced pressure from which it is pumped by a liquid pump to a liquid distributor header from 71 which:it is circulatedthrough cooling coils back to the refrigerant liquid tank, the combination of: electrical heating means interposed between the liquid pump and the liquid distributor header, said electrical heating means having associated therewith a normally closed relay switch adapted upon opening to interrupt the current to said heating means; a first conduit connecting said electrical heating means and the outlet of said liquid pump; a second conduit connecting said electrical heating means and the liquid distributor header; valve means for selectively controlling the flow of refrigerant liquid from the outlet of the liquid pump to the liquid distributor header or to said' electrical heating means; a thermostatic switch disposed in said electrical heating means, said thermostatic switch being connected to said relay switch and adapted to open the latter when the temperature of the refrigerant liquid within said heating means reaches a predetermined level; and a pressure switch connected to the refrigerant liquid tank and said relay switch for opening the latter when the pressure within said tank reaches a predetermined level. "7. In a refrigerating system the combination of a compressor having an inlet and an outlet; means for driving said compressor; a condenser connected to the outlet of said compressor; a refrigerant liquid tank connected to said condenser; a liquid distributor header; a pump having an inlet connected to said refrigerant liquid tank and having an outlet connected to said header; a plurality of cooling coils connected to said header and said refrigerant liquid tank; a suction line connecting said refrigerant liquid tank to the inlet of said compressor; liquid heating means having an inlet conduit connected to the outlet of saidpump and having an outlet conduit connected to said header; and selector valve means for selectively connecting the outlet of said pump to said header or to said liquid heating means. 8. In a refrigerating system the combination of z a compressor having an inlet and an outlet; means for driving said compressor; a condenser connected to the outlet of said compressor; a refrigerant liquid tank connected to said condenser; a liquid distributor header; a pump having an inlet connected to said refrigerant liquid tank and having an outlet connected to said header; a plurality of cooling coils connected to said header and said refrigerant liquid tank; a suction line connecting said refrigerant liquid tank to the inlet of said compressor; electrical heating means connected in heat transfer relationship between said pump and said liquid distributor header and having an inlet conduit connected to the outlet of said pump and having an outlet conduit connected to said header; and selector valve means for selectively connecting the outlet of said pump to said header or to said liquid heating means.

9. A refrigerating system as defined in claim 8 in which said electrical heating means has connected thereto a thermostatic switch adapted to inactivate said heating means when the temperature of the refrigerant liquid therein rises above a predetermined level.

, 10. A refrigerating system as defined in claimv 8 in which the refrigerant liquid tank has a pressure switch connected thereto, said pressure switch being connected to said electrical heating means for-deenergizing the latter when the pressure within the refrigerant liquid tank reaches a predetermined level.

11. In a dual cycle refrigerating system having a cooling cycle during which frost and ice progressively accumulate on the exterior surface of a plurality of cooling coils through which liquid refrigerant is circulated and a defrosting cycle during which said frost and ice are melted from said cooling coils, the combination of: a refrigerating apparatus including a compressor having an inlet and an outlet, means for driving said compressor, a condensor connected to the outlet of said compressor, a refrigerant liquid tank connected to said condenser, a liquid distributor header, a pump having an inlet connected to said refrigerant liquid tank and having a normally open outlet line connected to said header, a plurality of cooling coils connected to said header and said refrigerant liquid tank, a normally open suction conduit connecting the inlet of said compressor and said refrlgerant liquid tank; and a defrosting apparatus including liquid heating means having a first normally closed conduit connected to said outlet line of said pump, and a second normally closed conduit connected to said header, the closing of said suction conduit and said line and the opening of said first and second conduits causing a shift from the cooling to the defrosting cycle.

12. A refrigerating system as defined in claim 11 in which said liquid heating means has connected thereto a thermostatic switch adapted to lnactivate said heating means when the temperature of the refrigerant liquid therein rises above a predetermined level.

13. A refrigerating system as defined in claim 2 in which the refrigerant liquid tank has a pressure switch connected thereto, said pressure switch being connected to said liquid heating means for deenergizing the latter when the pressure within the refrigerant liquid tank reaches a predetermined level.

FELIX W. POWERS.

ALBERT LUNDIN.

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